Covalento rganic frameworks are an ew class of crystalline organic polymers possessing ah igh surfacea rea and ordered pores. Judicious selection of buildingb locks leads to strategic heteroatom inclusion into the COF structure. Owing to their high surfacea rea, exceptional stability and molecular tunability,C OFs are adopted for various potential applications. The heteroatoms lining in the pores of COF favor synergistich ost-guest interaction to enhance a targeted property.I nt his report, we have synthesized ar esorcinol-phenylenediamine-based COF which selectively adsorbs CO 2 into its micropores (12 ). The heat of adsorption value (32 kJ mol À1 )o btainedf rom the virial model at zero-loading of CO 2 indicates its favorable interaction with the framework. Furthermore, we have anchored small-sized Ag nanoparticles ( % 4-5 nm) on the COF and used the composite for chemicalf ixationo fC O 2 to alkylidenec yclic carbonates by reacting with propargyl alcohols under ambient conditions. Ag@COFc atalyzes the reaction selectively with an excellent yield of 90 %. Recyclability of the catalyst has been demonstrated up to five consecutivec ycles. The postcatalysis characterizations revealt he integrity of the catalyst even after fiver eaction cycles.T his study emphasizes the ability of COF for simultaneous adsorption and chemical fixation of CO 2 into corresponding cyclic carbonates.
Here, we report two novel water-stable aminefunctionalized MOFs,n amely IISERP-MOF26 ([NH 2 (CH 3 , which show selective CO 2 capture capabilities.T hey are made by combining inexpensive and readily availablet erephthalic acid and N-rich adeninew ithC ua nd Zn, respectively.T hey possess 1D channels decoratedb yt he free amine group from the adenine and the polarizing oxygen atoms from the terephthalate units. Even more, there are dimethyl ammonium (DMA + )c ationsi nt he pore rendering an electrostatic environmentw ithin the channels. The activated Cu-andZ n-MOFs physisorb about 2.7 and 2.2 mmol g À1 of CO 2 ,r espec-tively,w ith high CO 2 /N 2 and moderate CO 2 /CH 4 selectivity. The calculated heat of adsorption (HOA = 21-23 kJ mol À1 )f or the CO 2 in both MOFs suggest optimal physical interactions which corroborate well with their facile on-off cycling of CO 2 .N otably,b oth MOFs retain their crystallinity and porosity even after soaking in water for 24 hours as well as upon exposure to steam over 24 hours. The exceptional thermal and chemical stability,f avorable CO 2 uptakes and selectivity and low HOA make these MOFs promising sorbents for selective CO 2 capture applications.H owever,t he MOF'sl ow heat of adsorption despite having ah ighly CO 2 -loving groups lined walls is quite intriguing.
Adaptable polymer-based solid-state electrolytes can be a game-changer to safe, lightweight flexible batteries. We present a robust Bakelite-type organic polymer covalently decked with viologen, triazine, and phenolic moieties. Its flexible...
Carbon capture from industrial effluents such as flue gas or natural gas mixture (cf. landfill gas), the primary sources of CO2 emission, greatly aids in balancing the environmental carbon cycle. In this context, the most energy-efficient physisorptive CO2 separation process can benefit immensely from improved porous sorbents. Metal organic frameworks (MOFs), especially the ultramicroporous MOFs, built from readily available small and rigid ligands, are highly promising because of their high selectivity (CO2/N2) and easy scalability. Here, we report two new ultramicroporous Co-adeninato isophthalate MOFs. They concomitantly carry basic functional groups (−NH2) and Lewis acidic sites (coordinatively unsaturated Co centers). They show good CO2 capacity (3.3 mmol/g at 303 K and 1 bar) along with high CO2/N2 (∼600 at 313 K and 1 bar and ∼340 at 303 K and 1 bar) selectivity, working capacity, and smooth diffusion kinetics (D c = 7.5 × 10–9 m2 s–1). The MOFs exhibit good CO2/N2 kinetic separation under both dry and wet conditions with a smooth breakthrough profile. Despite their well-defined CO2 adsorption sites, these MOFs exhibit only a moderately strong interaction with CO2 as evidenced from their HOA values. This counterintuitive observation is ubiquitous among many MOFs adorned with strong CO2 adsorption sites. To gain insights, we have identified the binding sites for CO2 using simulation and MD studies. The radial distribution function analysis reveals that despite the amine and bare-metal sites, the pore size and the pore structure determine the positions for the CO2 molecules. The most favorable sites become the confined spaces lined by aromatic rings. A plausible explanation for the lack of strong adsorption in these MOFs is premised from these collective studies, which could aid in the future design of superior CO2 sorbents.
Coordination flexibility assisted porosity has been introduced into an Iron‐isonicotinate metal‐organic framework (MOF), (Fe(4‐PyC)2 ⋅ (OH). The framework showed CO2‐specific gate opening behavior, which gets tuned as a function of temperature and pressure. The MOF′s physisorptive porosity towards CO2, CH4, and N2 was investigated; it adsorbed only CO2 via a gate opening phenomenon. The isonicotinate, representing a borderline soft base, is bound to the hard Fe3+ centre through monodentate carboxylate and pyridyl nitrogen. This moderately weak binding enables isonicotinate to spin like a spindle under the CO2 pressure opening the gate for a sharp increase in CO2 uptake at 333 mmHg (At 298 K, the CO2 uptake increases from 0.70 to 1.57 mmol/g). We investigated the MOF′s potential for CO2/N2 and CO2/CH4 gas separation aided by this gating. IAST model reveals that the CO2/N2 selectivity jumps from 325 to 3131 when the gate opens, while the CO2/CH4 selectivity increases three times. Interestingly, this Fe‐isonicotinate MOF did not follow the trend set by our earlier reported Hard‐Soft Gate Control (established for isostructural M2+‐isonicotinate MOFs (M=Mg, Mn)). However, we account for this discrepancy using the different oxidation state of metals confirmed by X‐ray photoelectron spectroscopy and magnetism.
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